1. Field of the Invention
The invention relates to a fine and stable oil-in-water (O/W) emulsion containing ionic polymer particles and to its process of preparation. This emulsion can constitute a composition intended in particular for the topical treatment of the skin (body, face) and/or of the hair, in particular a cosmetic or dermatological composition, intended in particular for anti-sun protection. The invention also relates to the use of the emulsion according to the invention for the photochemical stabilization of chemical sunscreens and to the use of ionic polymer particles for the stabilization of a fluid oil-in-water emulsion.
2. Description of the Background
For various reasons relating in particular to their great comfort of use and to their freshness, cosmetic compositions, in particular those intended for the photoprotection of the skin against UV-A and UV-B radiation, known as anti-sun compositions, are generally provided in the form of an oil-in-water emulsion containing an oily phase dispersed homogeneously in an aqueous phase. In these conventional emulsions, which contain emulsifying (or surface-active) agents and optional cosmetic additives, the size of the globules constituting the fatty phase is generally greater than several microns. Such emulsions can have unsatisfactory cosmetic (oily feel) and physical (stability) properties.
Moreover, it is observed that, despite the presence of emulsifying (or surface-active) agents, some of these emulsions exhibit a lack of stability over time, a lack of stability which is reflected by the appearance of a separation phenomenon (phase separation) between the aqueous and oily phases of the emulsion. This instability is harmful to the storage of the emulsions.
Consequently, in order to avoid this undesirable phenomenon, it is often necessary to resort to so-called thickening agents which are then introduced into the emulsion, the main function of which is to create, within the aqueous phase, a gelled matrix which serves to set, within its three-dimensional network, the globules of the fatty phase, thus providing for mechanical maintenance of the entire emulsion. However, this addition of thickener limits the possible pharmaceutical dosage forms, excluding in particular very fluid compositions.
Now, there is an increasing search to prepare fluid compositions, in particular anti-sun compositions, more specifically with the aim of having available products which can easily evaporate, which products are often regarded by the user as easier to apply than creams.
Moreover, the presence of surfactants generally requires the emulsion to be manufactured with heating, which limits in particular the nature of the active agents to be introduced into the emulsion. In particular, this process excludes the use of heat-sensitive active agents. Consequently, attempts have been made, in addition to searching for fluidity, to dispense with surfactants.
It is known, from EP-A-0,692,237, to stabilize O/W emulsions with hollow particles of non-ionic polymer. However, hollow particles of this type, of non-ionic nature and with a size of the order of a micron, do not make it possible to obtain very fine emulsions, the oil droplets of which have a size of less than 500 nm. In addition, the particles described in this document require the presence of a gelling agent in order to improve the stability of the dispersion and do not make it possible to obtain very fluid emulsions.
Moreover, FR-A-2,681,248 describes compositions containing nanoparticles encapsulating an oil. Such particles can be incorporated in a preprepared emulsion but cannot participate in the preparation and in the stabilization of an emulsion because they can open during excessively vigorous agitation. In particular, they are not suitable for the production of very fine emulsions, that is to say containing oil droplets with a size of less than 500 nm.
In addition, the nanoparticles described in this document form capsules containing an oil and have the function of protecting the oil in the composition in order to release it only when applied to the skin. The oil therein is completely encapsulated in the film of the nanoparticles. The aim of the present invention is to obtain an emulsion where very fine oil droplets are not encapsulated but are distributed in the aqueous phase.